Hammer mill blade



Jan. 19,1932 P. P. BOWEN HAMMER MILL BLADE Filed Dec. 9, 1929 Bray i of said blades. 1 V

Patented Jam, 19, 1932 p 1 111111123 immanent.

Application filed necemter 9, 192 -1;sesa e 412E 4? 'This invention relates to that type of-dis integrating machine or 'pulverizer known as a fhammer mlll, and relates 'moreespec ally.

to this machine when so constituted as topul verize the materialfby. cutting or slashing rather than by *crushing the 'same." particular the invention relatesito" the cutting knives or blades of'su'ch a hammer mill and to the means o'fobtaining the maximum cut- 1 ging eificiencyandoperating economy there r,om.-k"l

Theobjectof the invention istoprovide a hammer mill blade which will; cut 0rv pulver ize' alarge quantity of material-per hour with a minimum power expenditure; Vwit h a lo w cost of maintenanceand replacements {and with aminimum loss-of time due to shut downs.

, "Inthe 'accompanying drawings:

. througha typicalhammer mill pulverizer showing a plurality "Ofthe improved hammer spaces between said grid bars 'andl'to'be re':

'ceived within the]pulverizedmaterial pit 21', whiohis arrangedbebw the grid bars and in' usual practice, is subject to a vacuum action 1 to ensure the rapid movement of pulverized mill blades installedfthereinp j p Figure 2 is an enlarged perspective'of one Figure 3 is an enlarged perspectiveof a modified form of blade; p

Figure 4 is an enlarged layout of the improved bladein'relation to the'power sha of the hammermill,illustrating the geometric values 'ofthe cutting face of said blade.

Figure 5 is a considerably enlarged frag-1 mentary side view of one ofthe'hammer mill blades showing a modified form of cutting face which has a small, positive cutting angle;

Similarcharacters. of referenceindicate like parts in'zeach of the several views. 1 1

Figure 1' illustrates a typical hammer mill 0 pulverizer having a main frame 10in which is suitably journaleda power shaftf11', the

" latter being-fadap'ted to be suppliedwith power from an external source inany suitable manner. Secured by a key 12 or otherwise to said power shaft are a plurality of flanges l3qwhich' are disposed transversely to and project out from said power shaft and are preferably provided at their central portions with hubs 14 in the usual and well known Disposed parallel to and concentric with a pluralityof hamnierjmill"blades 16, which Figure l is a vertical-transverse section same being preferably symmetrical about 22 which is adaptedtoembrace a companion a; amine;1151 3 1 amer rb'wigof 5' piyot. shafts 15 whichflare suitably secured toand aretherebyrotatedwithaforesaid' ro I tor flanges 13 andgthepowershaft11; QPiV- otally :mounted upon :saidpivot shafts 1 5 Lare are thrown" outwardly by centrifugal 'l 'fdrce into the position of Figlfl whenever they :are rapidly rotated together with" the ower shaft 11 androtor'flanges l3. v

The material to be pulverized or disintew grated is'ifed into" the hopper 17 at the upperpart ofthe' machine and flows down upon "a beater plate-'18 arranged adjacent to the downward'path of the blades where the ;ma-;

iterial receives arapidsucoession of violent slashes from the rapidly revolving blades Theslashedmaterial isthence'thrown or "car v rid down upon a plurality of'grid bar- 1120 a which are suitably spaced from, eachf othe'rto 7. M

allow 'any certain desired size-of pulverized; material to fall or to be sucked ,through the material through said gridbars 20." Any magrid bars a'ndnotbut into sufliciently fine pieces' 'while lyin'gthereon, is thrown; up and around with the-bladeslG and again falls upon the beater; plate 1 8 and'again slashed v and "from thence ag'ain" thrown upon the aforesaidgridfbars 20. i, i i i 1.6, which-arepre'ferably punchedor stam' d from sheet metal into the form shown in ig: 2, theopposite ends, faces and edges ofthe their long-itudinal transverse and perpendicularaxes, for reasons'which will: appear laters On" what we may, for convenience, call the inner end'o'f the blade is formed a pivot hole, 5

pivot shaft 15 *so as to';bepivota-lly-connected I therewith." Assuming-howga counter clock-Q wise rotation as Fig. 1], it is evident thatthe cuttingaaction ofjthe. bl'adewill} occur-at the lower right hand corner of the blade as shown mo tg5. Thepresentjinventionresidesin thebladesi. v

in Figs. 2 to 5 inclusive, i. e. at the outer portion of the advancing side of the blade which outer portion thereby acts as a cutting face 23*. It is here assumed that the material being handled is capable of being slashed and not merely and solely pulverized by impact the latter condition not being within the purview of the present invention. 7 v

To ensure proper cutting action, it is very desirable that this cutting face 23 have the proper top rake,.i. e. that said cutting face be disposed at a proper angle relative to a radius 24 passing from the axis of the power shaft 11 out to the outer corner 25% of the blade. The proper selection of the angle for l the said'cutting face is properly a function of this radius 24, but thisangle may also be defined as relative to the axis or the parallel sides of the blade. For some classes of material, maximum cutting efficiency is obtained with the form of blade 28 (shown in Fig. 5) by the use of a very slight positive rake, i. e. of a. cutting face 125 having a top rake which is positive (or mathematically plus) relative to said radius 24. In other words the top.rake or cutting face angle of the blade shown in Fig. 5, (which, of course, passes through the outer end 125" of said cutting face) is so disposed as to-make a slight angle in a clockwise direction from the'radius 24 aforementioned, about the said outercorner 125 as-a center of rotation. If the said cutting face were toliein a plane coincident with the outer,parallel edges of the blade, the value of the cutting face angle (seeFig. 4) would be positive and equal to the angle whose sine is one-half the width of the-blade divided by the length of the radius 24 from. its origin at the axis ofthe power shaft 11 out to the outer corner 25 of theactive cutting face 23*. It is, however, the object of this invention to not have so great a positive rake as this, but, instead, to have eithera' smaller positive rake as in Fig. 5 or a small negative rake as in Fig. 4, the latter being preferable when pulverizing most classes of material. 7 Thus in most uses of the hammer mill it is preferable to have the cutting face 23 make a small negative angle with the radius 24, asshown particularly in F 1g. 4'; 1. e a maximum of cutting efliciency is obtained by having the cutting face angle (which passes through. the outer corner 25 of the blade) make a small counter clockwise angle with said radius 24 and with said outer corner 25 'as a theoretical center. Thisensures that all material cut up by the extreme corner 25 of the blade is caused to be pushed inwardly toward the axis of the power shaft 11 and thusaway from the said corner 25 so that the latter is caused, in effect, to be self-clearing and always in condition to take fresh new bites on a succession of pieces of material.

In the course of time, however, the cutting face 23 ofeachhammer mill blade will become dull, and this invention contemplates the successive resharpening of said cutting face which is defined by the indicating line 24 all ofsaid resharpenings being obviously rendered possible without taking any of the cutting blades out of the hammer mill.

The said indicating line 24 which defines said final cutting face may be physically marked on the surface of the blade in any suitable manner, preferably by a slight groove or a fin formed upon one or both faces of the blade by suitably forming the dies which perform the punching or stamping operation. For purposes of illustration, the width'and depth of the indicating. line has been very considerably exaggerated in the drawings, only a very faint line or fin being required in practice. Said indicating line may, if desired, be formed by etching filing, prick punch marking or otherwise.

. 7 TV hen the saidrfinal cutting face at 24 of any one blade becomes excessively dull, it is obvious that usually all of the'final cutting faces of all the other blades 16 have become dull too, in which case all of the pivot shafts threading off all of said blades from their companion. pivot shafts-15I Thereupon, the pivot hole 22 may again be employed to pivotally connect each blade with its companion pivot shaft 15, but in this case, with each blade turned backwards from its initial position, that is with the other. longitudinal edge positioned forwardly, so that the cutting face 230 now becomes the active cutting face. This face is in turn ground back successively as each previously ground cutting face becomes dulled through use, until the grinding recedes to the indicating line240.

When this secondary final cutting face 230, now ground back to indicating line 240 becomes toodull, the whole blade is again removed from its companion pivot shaft 15 and each blade turned-end for end so that the pivot hole 22 acts as the pivot for each blade upon its companion pivot shaft. In practice all of the blades are usually simultaneously thus turned end for end in this manner. It isobvious that this change has furnished another pair of cutting faces 23 and 230 which are adapted to be successively ground back in the same manner as cutting faces 23 and 230. To state the matter more broadly, theblade is so formed as to be symmetrical about all threeof its axes, so that either end may be disposed outwardly and, in each of the latter two positions, either of the two edges may be disposed forwardly, so that the effect is that each blade has four cuttting faces, with two. faces at each end of each of its side edges.

It will be noticed that the opposite ends 26 and 26 of each blade are symmetrically curved, the radius of said curved ends being this means the clearance approximately the distance out from the axis of the power shaft 11 when the blade is normal operating position,.as in Fig.1. By

between all the four outer corners 250 '25 and 250 of the cutting faces, as said faces are successivelymaintain a very small minimum clearance at V the center of the blade, this radiusmay be reduced somewhat, inwhich casethe clearance will not remain precisely uniform (in I the normal position of the blade) as the cut-- ting face is ground back, but the'minimum clearance will (as in this case desired) be smaller. This state of afiairs does not-exist if the blades are pivoted. directly upon the power shaft, as is obvious, and it is within the purview of the present invention that the blades be so mounted special classesof material.

\A modified form of blade 27 is shown in Fig. 3 in which additional cutting faces 28*, 280", 28* and 280 are added at the central portions of the ends of the blade. This modified blade is more particularly adaptedfor pulverizing very light flocculent material. In: blade constituting the present invention is of considerable commercial value in that provif sion is made for success vely sharpeningthe cutting faces and with these successive l'opy erations conveniently performable without hammer mill,

dismantling any part ofthe as is now customarypractice. Furthermore,

-' with the usual construction of the present invention, this successive grinding back of the cutting face does not alter the clearance between-the outer ends of said cutting faces and the grid bars of the hammer mill. In addition to this, provision is made for most advantageously using all four corners of each blade so as to enable each toserve insuctherebyconsideracession as a cutting face,

bly extending the life of each blade and increasing the economy of operation. Furthermore suitable provision ismade for clearly indicating the maximum amount of grinding to be allowed so that the re-grinding operation may be placed in the hands" of unskilled workmen. Besides this,'the blade is of such form as to be readily produced bya single punching or stamping operat on.

I claim as my invent on:

A blade for hammer mills having a body V of sheet metal providedadjacent to its op- .-for the grinding of j general, the novel form of hammer mill posite ends 1 with pivot body ona rotary support, and opposite ends of said body being curved continuouslyand concentrically. with the axis of said rotary.

support whenteitherendof the body isin the said body having opposite r parallel'longitudinaledges and-inclinedfaces I,

{one of-which may operative-position,

at its four corners any be broughtiinto the operative position and openings eitherfofwhich is adapted to. pivotally' moiint said If eachofwhic-h recedes at an angle from one corner of the body and isarranged inwardly from the respective longitudinal edge of the bladebody g In testimony diedi Thereby dnx myfsig- I nature.

V lesson-P,- BOWEN- 

